This application is a continuation-in-part of application Ser. No. 456,323 filed Mar. 29, 1974, now abandoned.
The use of carbon discs as a friction element in a wheel and brake assembly for aircraft has gained acceptance as a way of increasing the payload and increasing effectiveness of a braking system.
In U.S. Pat. No. 3,639,197 assigned to the same assignee as the invention and incorporated herein by reference, it is disclosed how a continuous carbon fiber can provide a carbon disc with the structural unity needed to absorb reported braking torque. Such a carbon disc when used in aircraft braking systems can often experience thermal conditions above 800.degree.F. Above 800.degree.F the non-swept areas of the carbon disc are subject to oxidation which can cause a complete disintegration of the carbon matrix and continuous carbon fiber resulting in a brake failure.
In U.S. patent application Ser. No. 324,624, now U.S. Pat. No. 3,914,508 incorporated herein by reference, a method is disclosed for protecting a carbon substrate in a moist environment from oxidation by coating a selected surface thereof with a boron and metallic mixture which is held therein by a resin matrix. As with most coatings it was difficult to maintain uniform thickness over the entire peripheral surface. As a result where the coating is limited or absent, deterioration of the carbon substrate will take place after a period of time during a brake application sequence.
In another patent a metal ring was press fit around the outer periphery to prevent the oxidation in the non-swept area of a carbon friction disc. During frictional operation when the thermal energy produced was low, the unit operated effectively. As the temperature increased, the unity of the carbon disc and steel ring changed in direct proportion to the differences in their thermal coefficients of expansion. After a repeated number of frictional engagements at high temperatures, structural defects in the metal occurred along the periphery of the carbon disc because of the different coefficients of expansion.